Re: 485 super weak brightness control


Ondrej Pavelka
 

In the last paragraph you mentioned 2x multiplier but what we observe is
10x, does it still make sense to look in this part of the circuit?

On Fri, 19 Mar 2021, 22:47 Ondrej Pavelka, <info@vintageaudiorepairs.eu>
wrote:



On Fri, 19 Mar 2021, 22:18 Ozan, <ozan_g@erdogan.us> wrote:

I noticed when I move the picture all the way to the left in 521 mode
there
is something on the screen but it's all crooked
I can think of two possibilities: B sweep delay is not reset to zero in
5/2/1n mode (there is a circuit to do that), or there is a little circuit
that shifts the screen left in B sweep mode (Q1331 in <11>) that is not
working
Great feedback, I will check this out on Monday


Delay not set to zero:
In 5/2/1n mode B timebase is used but delay is set to zero. It could be
that the delay is applied still because of some issue. On <7> switch A9
opens in 5/2/1n mode to set time delay zero independent of delay knob. It
is possible the delay pot is dirty and not making a good contact. What
voltages do you see at pin 3 of U910 and base of Q902B in 5/2/1n mode?

I don't think pot is dirty because I can smoothly and without any jumping
adjust delay on the presets where I can see both A and B sweeps



B sweep shift:
B18, B22, B1-4, control left shift of trace in B sweep. You can check B18
and B22 by measuring voltages at J3 and J5 on sheet <11>

Great suggestion, I will check that on Monday


I looked at A sweep, A gate, and B gate signals on my 485. A sweep and A
gate signals stay same as 10ns setting when you are in 5/2/1n. When in A
sweep B gate is not there until you hit 5/2/1n, then B gate starts at the
same time as A gate (zero delay).
This is exactly what I observed on A gate and A sweep, I haven't checked
the B sweep connector


I remember you didn’t see A gate in 5/2/1n. Could you re-measure again
between 10ns and 5ns settings? May be "B ends A" is active although 5/2/1n
should turn it off. On front panel you will see “B ends A” next to the
hold-off knob. Does it make any difference if it is not in “B ends A”? If
it does A2 switch on <9> is dirty.
That is not correct, I was able to see the gate signals but they only
haven't changed. Same as you described above


B sweep in the positions 10us to 0.2us is showing it 10x wrong
I read as B sweep runs slower.

Correct



So 100ns is shown as 1us
Is 0.1us also 10x slower? Above statement was for 10us to 0.2us.
I used bad example time, I wanted to make sure we know in which direction
slower / faster


How is 2ms, is it also 10x slower?
I can't see it so I can't tell you, long times are not showing me anything
then I have a set of times which are shown as slow then I get correct times
but truncated


You may want to check relay K1241, caps C1443, C1442.

Switch B18 turns on a 2x multiplier, if it is not working you will get 2x
slower.

Good one I'll check that



Ozan





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